Mountain biking is a very popular sport throughout the United States and the world. In order to provide a more comfortable ride, mountain bike riders often will ride dual suspension bicycles. Dual suspension bicycles have a biasing member (often called a shock absorber) at the front of the frame to dampen biasing member generated by the front wheel and a biasing member absorber connected to the main frame and/or rear frame (generally the rear triangle) of the bicycle to dampen biasing member from the rear wheel of the bicycle. The latter is generally called a rear suspension bicycle. A rear suspension bicycle utilizes a linkage system to link the rear triangle of the bicycle to the main frame of a bicycle in combination with a biasing member absorber. The arrangement of this linkage system directly affects the performance of the rear suspension of the bicycle. Thus, the rear suspension can be designed in a variety of layouts for a variety of purposes.
A prime concern when designing a rear suspension system is to assess the performance of the rear suspension for an intended use of a bicycle bearing that suspension. For example, in a bicycle designed for traveling both uphill and downhill, an ideal design will allow the rear suspension to provide sufficient dampening of shock while traveling downhill, yet minimize the negative effects caused by the rear suspension when a mountain bike rider is traveling uphill. These negative effects include, for example, the tendency of a rear suspension bicycle to compress under acceleration, which creates inefficiency in pedaling as force is lost due to the compression of the rear suspension, and in some designs the tendency of the shock absorber to extend and exert force upward on the mountain bike rider. These phenomena are well known and attempts to overcome them are generally called anti-squat. Anti-squat thus seeks to maximize the efficiency of the rear suspension by seeking to maximize the amount of pedaling or acceleration energy translated into forward motion. Thus a bike with a high anti-squat has a lower tendency of the shock absorber to compress while a bicycle with too high of anti-squat has a tendency of the shock absorber to exert force in the opposite direction of compression, also known as extending.
However, maximizing anti-squat can come at a disadvantage in that if a bicycle has too much anti-squat, it can lead to an extension of the rear shock in response to a user pedaling and/or pedal kickback when the suspension compresses when a user is accelerating over bumps in the trail.
To measure the anti-squat principles of a bicycle or other wheeled vehicle, the instant center (or “IC”) of the rear suspension is measured. The instant center of a bicycle has a common meaning in the bicycle industry, but in general is defined as an imaginary point about which the rear axle is rotating around at any given instant. The IC moves or migrates as the rear suspension compresses. The assembly of the rear suspension is designed in order to provide an IC migration, and thus anti-squat behavior, in response to a given condition. Thus an ideal bicycle rear suspension for a bicycle utilized for both uphill and downhill riding, such as cross country riding, that is supple and shock absorbent when traveling downhill yet efficient and feels as close to “locked”, or in performance terms as similar to a bicycle lacking a rear suspension, as possible when under either pedal power or motor power. In general a line denoting the IC across the range of compression of a bicycle suspension indicates a stiffer suspension across compression if the line moves up and/or back whereas an IC line moving down and typically forward indicates a less stiff suspension.